Two-pass regenerative air preheater



D. YERRICK 2,480,277

TWO-PASS REGENERATIVE AIR PREHEATER Filed Aug. 22, 1946 PREHEATED AIR OUTLET A TORNEY Patented Aug. 30, 1949 TWO -PASS REGENERATIV E AIR PREHEATER William D. Yerrick,

The Air Preheater Corporation,

Wellsville, N. Y., assignor to New York, N. Y.

Application August 22, 1946, Serial No. 592,320 4 Claims. (01. 25'l6) The present invention relates to heat exchange apparatus and particularly to improvements in a regenerative heater of the rotary type.

Rotary regenerative heaters such as those of the Ljungstrom type comprise a rotor carrying heat transfer material which is first moved through a gas passage to absorb heat and then moves through anair passage to impart heat to the air which flows through the preheater in counterflow with respect to the heating medium. The gas and air ducts in such a preheater are in communication to openings in sector plates at the opposite ends of the rotor and the latteris divided by radial partitions into a plurality of wedge-shaped compartments in which the heat transfer material in the form of plates are mounted. To prevent mingling of the streams of gas and air the partitions are conventionally provided with sealing members which bear against the opposing faces of the sector plates to seal the gas and air passages from each other. However, because the rotor turns at relatively slow speed it becomes unequally heated since it is exposed on one side of its axis of rotation to the heating gases and on the other to cold air or other fluid to be heated; and further the heat exchange process necessarily entails a considerable differential between the temperatures of the entering and leaving gas and'air streams at the inlet and outlet ends of the rotor. All of this has the effect of causing a bulging or distortion of the-rotor which displaces the sealing members from good sealing contact with the sector plates.

An object of the present invention is to pro-' vide an improved preheater construction in which distortion of the rotor due to temperature differentials is minimized with resulting improvement in the effectiveness of the sealing members. 1

Another feature of the present invention is a heat exchanger: construction in which the effects of corrosionon the certain sections of the heat transfer plates due to cooling by the gases. is

minimized.

Other features and advantages of the present invention will become apparent upon considers tion of the following detailed description of an illustrative embodiment thereof when read in conjunction with the accompanying drawing in which: i

Figure 1 is a sectional elevation of a Ljungstrom type preheater embodying the present invention;

Figure 2 is a planview corresponding to Figure 1;

Figure 3 is a fragmentary view scale illustrating a sealing device; and

Figure 4 is a diagrammatic view illustrating the distortion of a preheater rotor due to temperature differentials between its inlet and outlet ends.

In the drawings the numeral l0 designates the preheater housing within which is mounted a rotor designated as a wholeby the numeral ll adaptedto be slowly rotated within the housing on its axis I! by a motor l3 operating through reduction gearing. conventionally the rotor H consists of a cylindrical shell it connected by radial partition plates l5 to the rotor post. l2. The radial partitions divide the interior of the rotor lntovwedge-shaped compartments each. of which contains a multiplicity of spaced metallic plates [6 which absorb heat from hot gases passed thereover and then impart it to air or other fiuid to be heated. Usually the-wedge-shaped compartments .are subdivided by circumferential diaphragms ll. v p

conventionally the heating gases and the air to be heated flow countercurrent to eachother at opposite sides of the axis l2 of the rotor, being admitted to and taken from the housing l0 through ducts connected into openings iii-the sector plates 2|] mounted on the housing Ill at opposite ends of the rotor as'indicated in Figure -4. With heating gas entering at say 1500" F. and

being discharged at 500 F. while air enters at F. and is heated to 1000 F. it will be seen that there is a temperature differential of 1000 between the gas inlet and discharge ends of the rotor and nearly as great a diiference between the air inletand outlet sides of the rotor. As a result, the rotor is hot at one end and cool at the other so that unequal expansion takes place causing a distortion of the rotor as a mass, which dishes it somewhat as indicated in Figure 4. A consequence of this is that the parts of the radial seal members I 9 on the radialpartltions l5 are withdrawn from proper wiping contact .or like cooperation with the imperforate portions of the sector plates 20 and the gases may leak into the air stream by crossing over inlthe space between the ends of the rotor and. the opposed faces of the sector plates;

According to the present invention the rotor II is provided at a point inwardly of the shell vll with a circular partition 29 which dividesthe rotor into inner and outer annular sections 25, 26 radially spaced from each other. Partition 29 is positioned at a radial location such that the flowarea is substantially the same in the inner on an enlarged and outer sections, or somewhat greater in the latter to accommodate larger volumes hot gas and heated air. On the upper end edge of this circular partition there are mounted circular sealing strips 21 which cooperate .with a similar outer side of partition 21 and above section 26 of the rotor to provide for the admission at the upper end of the rotor of hot gases supplied through a duct 22 connected to the upper end of the housing l0. Beneath the rotor ll an extension 23 of the housing l0 forms a chamber 24 so that gas flowing downwardly over the heat exchange plates It in the outer section 25 01' the rotor may pass around the lower end of the circular partition 29 and reversing its direction flow upwardly over the heat exchange plates in the section 26 of the rotor to be discharged through an opening 30 in the end plate 24 into a gas outlet duct 3| suitably connected to the upper end of the housing inwardly oi the gas inlet duct 22 and between the latter and the rotor post l2.

The air side of the heat exchanger is of generally similar construction, the cold air being admitted however to the inner section 28 of the rotor on the opposite side oi. the rotor post through an inlet duct 34. The air flows through sector opening 32 and downwardly through section 26 to reverse its direction in a chamber 33 on the opposite side of the rotor post from the chamber 24 and then flows upwardly over the heat exchange plates in the outer section 25 01' the rotor through sector opening 35 into a chamber 36 located on the top of the housing I. In the arrangement shown the heated air is taken from the chamber 36 through the dual outlet ducts 3'! connecting into the ends of chamber 34.

The sector plate 203 opposite the lower end of the rotor has only a pair of apertures, one each on the gas and air sides and separated by the usual imperiorate portion against which the radial seals I! bear.

An auxiliary ofl'take duct 4| connected to chamber 33 permits heated air to be taken from this chamber 01' the preheater for uses requiring a temperature less than the maximum aflorded by passage of air through section 25 as well as section 26.

Hoppers 38 are provided on the underside of the housing in communication with the chambers 24 and 33 to receive fly ash, dust and other material that may be separated out in the reversal of direction of flow of the gas and air and 'also to receive soot and other impurities cleaned from the rotor by a cleaning apparatus 39 on the air side.

The construction above described minimizes d stortion of the rotor as a consequence of temperature diflerentials between the upper and lower sides thereof. This is due to the fact that the streams oi gas and air by flowing in two passes over the heating elements ll in the rotor produce more equalized temperatures at opposite ends of the rotor I I than is the case where the stream of gas, with counter-current air, is admitted, for example, at the under side of the rotor and after passing over the heat exchange material is discharged at the upper end thereof as shown in Figure 4. Herein for example, gas admitted to the inlet 22 at say 1500 degrees F.

could be reduced to 1000 F. in the chamber 24 as a result of passing over the heat exchange plates It in the outer section of the rotor. Then in passing through the inner section 2! of the rotor the temperature oi! the gases would be further reduced to say 500 F. with the result that the mean temperature or the rotor both on the upper and lower sides thereof would be approximately 1000 F. Likewise on the air side of the rotor air entering at a temperature of 80 F. would be heated to say 540 F. in passing through the inner section 26 of the rotor and further heated to 1000 F. in passing upwardly over outer section 25 oi. the rotor. Here also a mean temperature or approximately 540 F. would exist both on the upper and lower sides of the rotor on the air side thereof. As a consequence of this, distortion of the rotor due to extreme temperature differences between its upper and lower sides is considerably reduced.

Another advantage of the invention is that cleaning of the heat exchange plates I6 is facilitated since it is necessary to wash or blow air or steam through a relatively short distance that amounts to only one half or less of the depth of heating surface that would be required in a conventional type heater where fluids are admitted to one end of the rotor and passing once therethrough are discharged from the opposite end. A concomitant advantage is that the cleaning of the rotor may ordinarily be limited to its inner section 26. This is the section of the rotor containing the so-called cold end elements, i. e., those contacted by the coolest gases and the colder air. The construction described also localizes in the center section of the'rotor those heat exchange plates 40 which may be subjected to the greatest cooling action and thereby reach a temperature below the dew point oi the gases so that corrosion takes place. Thus, a further advantage is that if the heat exchange plates do become clogged and corroded the amount of surface that need be replaced is minimized and substantially less than would be the case in the conventional heater because the upper ends of the outer sections 25 are no longer involved. Inasmuch as the depth of the surface to be replaced or cleaned is reduced by one half compared with that of the conventional heater, it is possible to obtain higher heat recovery from the gases and risk cooling them to a temperature below the dew point because although condensation and resultant deposits of corrosive elements may possibly occur, the damage is minimized since the amount of surface that need be replaced is substantially less than in previous constructions.

What is claimed is:

1. In apparatus of the type described having a housing containing a rotor turning about a vertical axis; partition means dividing said rotor and housing into inner and outer annular sections; inlet and outlet ducts for one fluid connected to. said housing at the upper end thereof at one side of said rotor axis and communicating respectively with the outer and inner sections of said rotor; means forming a chamber in said housing below said rotor in communication with both the inner and outer sections of said rotor at said one side of said axis so said one fluid may flow in series through said sections via said chamber; inlet and outlet ducts for another fluid connected to said housing at the upper end thereof at the opposite side of said rotor axis; means forming a second chamber interconnecting the lower ends of the sections of said rotor at the opposite side of said axis for series flow of said second fluid therethrough; fluid sealing means associated with said housing and said rotor located between said fluid inlets and related outlets; and means maintaining the streams of fluid separated.

2. In a rotary regenerative heat exchanger having a housing containing a rotor carrying heat transfer material; partition means in said rotor sub-dividing it into a pair of parallelly arranged sections for fluid flow therethrough; fluid sealing means associated with said housing and said rotor located between said parallel flow sections at one end of the rotor; inlet and outlet ducts for a heating gas so connected to said housing at one end of the rotor as to communicate with corresponding ends of said sections; means forming separate stationary chambers at opposite sides of the rotor axis at the opposite end of said rotor for placing said parallel rotor sections in fluid communication with each other at their opposite ends whereby fluid flows through said rotor sections in series; inlet and outlet ducts for air or other fluid to be heated both connected to said housing at one end thereof for passing air through said sections in series; and cooperating sealing means on the rotor and housing for maintaining the streams of heating fluid separated from the stream of fluid to be heated.

3. In a rotary regenerative heat exchanger having a housing containing a rotor carrying heat exchange material; a circular partition dividing the rotor into inner and outer annular sections; cooperative fluid sealing means between said partition and said housing at one end of the rotor; gas inlet and outlet ducts connected at one side of the rotor axis to said housing at one end of the rotor for admitting a heating gas to one of said sections and for withdrawing it from the other; inlet and outlet ducts spaced circumferentially of said housing from said first ducts and connected to said housing at the opposite side of said axis for admitting and withdrawing air or other fluid to be heated; means formin separated chambers positioned at opposite sides of said rotor axis at the opposite end of the rotor in communication with both annular sections of the rotor so that fluid flowing through one annular section passes through the adjacent chamber to flow in series through the other annular section of said rotor; and means maintaining the gas stream separated from the air stream.

respectively with the outer and inner sections.

of said rotor; means forming a chamber in said housing below said rotor in communication with both inner and outer sections of said rotor so said gas may flow in series through said sections via said chamber; inlet and outlet ducts for air connectedto said housing at the opposite side of said rotor axis; means forming a second chamber interconnecting the lower ends of the sections of said rotor for series flow of said air therethrough; means maintaining the streams of gas and air separated; and hoppers connected to the bottoms of said chambers for receiving material separated from said streams of gas and air as the streams flowing downwardly through the outer sections of said rotor change direction in said chamber to flow upwardly throughthe inner sections of said rotor.

WILLIAM D. YERRICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'IENTS' Number Name I Date 1,759,916 Riley May 27, 1930 1,820,199 Riley Aug. 25, 1931 

